1. Field of the Invention
The invention concerns a vaulted cover to close a vertical recess in a pressure vessel with a plurality of fittings welded to the cover for the passage of steam pipes and with heat insulation applied to the inside of the cover, consisting of a thermally insulating material and a plurality of rectangular cover plates arranged on the thermally insulating material wherein the cover plates are fastened to the cover by means of holding bolts penetrating the entire insulation.
2. Background of the Prior Art
Covers of this type are used for example to cover components of nuclear power stations, such as steam generators or coolers, wherein high temperatures are prevailing. The covers are, therefore, provided with heat insulation. The layout of such an insulation represents a difficult technical problem, as the covers have numerous passages for steam pipes disrupting the insulation in these locations. Furthermore, the large differential thermal expansion of such a vaulted cover and the metallic covering of its heat insulation must be considered. In order to avoid the exposure of the holding bolts to excessive bending stresses, the covering must be subdivided into a plurality of plates.
The state-of-the-art shows thermally insulating devices on walls exposed to a gaseous heat carrier. Thus, from West German Offenlegungsschrift No. 21 59 781, heat insulation for the pressure vessel of a reactor is known, comprising several layers of a highly porous metal mesh and thin metal sheets located between said layers. The insulation is covered with holder sheets fastened by means of bolts to the liner of the pressure vessel. A number of gaps between the individual plates of the insulating material resulting from manufacturing tolerances, connect the layers of mesh under pressure with the heat carrier.
In West German Offenlegungsschrift No. 29 14 040, another thermally insulating device applied to surfaces of a nuclear reactor is described, consisting of several layers of a metal fabric or metal screens, separated by intermediate sheets of metal and assembled into panels. The tables, covered on their circumference with sheathing, abut on one side against the surface to be protected and are covered on the other side by a supporting sheet. The panels and the supporting sheets on the surface to be protected are secured by means of hollow bolts with nuts screwed onto the "hot" end of said bolts.
It has also been proposed to provide the fastening bolts of such thermal insulations with spacer sleeves, resting with one end on the surface to be protected and with the other fixedly supporting the holding sheets or cover plates. Supports are arranged so that the thermal expansion of the cover plates is not hindered.